This invention is an improvement over that disclosed in U.S. Pat. No. 4,032,777 granted to the same inventor, and the brief survey of monitoring devices and their shortcomings contained therein is applicable to the present invention. Although the monitoring device disclosed therein is adequate for many uses, it has been found to provide less than satisfactory operation in the presence of gaseous discharge lighting equipment, such as flourescent lights, and in low levels of light intensity.
As is well-known to those skilled in the art, gaseous discharge lighting devices actually turn "on" and "off" at a rate equal to twice the frequency of the power line frequency. Although this causes "flicker", it is not noticed by most individuals because it is substantially higher in frequency than the response of the optic nerves. However, it can cause eyestrain, problems when taking motion pictures or working with rotating machinery or rapidly moving elements and, under certain conditions of light intensity and/or circuit sensitivity, the circuit of the invention disclosed in U.S. Pat. No. 4,032,777 may respond erratically or inappropriately to the aforementioned flicker of said gaseous discharge lighting devices.
The improved circuitry of the present invention does not exhibit these problems.